Refrigeration system

ABSTRACT

A refrigerating system comprises a compressor, a condenser, an expansion valve, an evaporator, sensors for detecting respectively a temperature and a pressure of a refrigerant sucked into the compressor, and a pressure of a refrigerant discharged from the compressor, a liquid injection system including an injection passage and a flow control valve connected in the injection passage, and a control means for estimating a temperature of gas refrigerant discharged from the compressor, from detected values delivered from the sensors, and for delivering an instruction for controlling the injection quantity of the liquid refrigerant, depending upon the estimated temperature, to the flow regulating valve, thereby it is possible to control a temperature of the discharged gas from the compressor to a set value, irrespective of an operating condition.

BACKGROUND OF THE INVENTION

The present invention relates to a refrigerating system, and in particular to a technology of controlling a temperature of a refrigerant discharged from a compressor by injecting a liquid refrigerant into the compressor.

A refrigerating system is composed of a compressor for compressing a refrigerant, a condenser for condensing the compressed refrigerant, a depressurizing means for depressurizing the condensed refrigerant, and an evaporator for evaporating the depressurized refrigerant so as to cool the air in the refrigerator or the like.

In such a refrigerating system, it is required to restrain the temperature of a gas refrigerant discharged from the compressor (which temperature will be hereinbelow referred to “discharged gas temperature”) from exceeding a set temperature in order to prevent deterioration of a refrigerant and lowering of a viscosity of refrigerating machine oil contained in the refrigerant. Accordingly, a discharged gas temperature is detected by a discharged gas temperature sensor, and a liquid refrigerant is injected into a refrigerant in the compressor during compression stroke by a liquid injection means if the detected temperature is not less than a set temperature (For example, refer to JP-A-09-159288).

By the way, since the pressure of the refrigerant sucked into the compressor is low and the density of the refrigerant is low, the heat capacity of a gas refrigerant discharged from the compressor is small. Thus, in an unsteady-state condition upon, for example, a start of the compressor, the temperature of the gas refrigerant is lowered since the gas refrigerant discharged from the compressor makes contact with a pipe line and the like which therefore absorb a heat therefrom before it comes to a temperature sensor. As a result, a temperature difference between a temperature detected by the temperature sensor and an actual discharged gas temperature is caused until the temperature of the pipe line and the like increases up to a temperature in a steady-state condition.

However, similar to the refrigerating system as disclosed in the JP-A-09-159288, in the case of such control that a liquid refrigerant is injected into a compressor in dependence upon a detected value by the discharged gas temperature sensor, a delay would be caused at a start of the control, and accordingly, the discharged gas temperature would possibly exceed a set temperature.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to control the discharged gas temperature to a set temperature, irrespective of an operating condition of a refrigerating system.

To the end, according to the present invention, there is provided a refrigerating system comprises a compressor sucking a refrigerant for compressing the refrigerant, a condenser for condensing the refrigerant discharged from the compressor, a depressurizing means for depressurizing the condensed refrigerant, an evaporator for evaporating the depressurized refrigerant, a liquid injection means for injecting a liquid refrigerant into the compressor, sensors for detecting respectively a temperature and a pressure of the refrigerant sucked into the compressor, and a pressure of the refrigerant discharged from the compressor, and a control means for controlling an injection quantity of the liquid refrigerant, depending upon detected values delivered from the sensors, wherein the control means estimate a temperature of the gas refrigerant discharged from the compressor, depending upon the detected values delivered from the sensors, and delivers an instruction for controlling the injection quantity of the liquid refrigerant, depending upon the estimated temperature.

That is, an energy inputted to the compressor equally balances with an energy outputted from the compressor, and accordingly, the temperature of a gas refrigerant discharged from the compressor (discharged gas temperature) can be obtained from a temperature (inlet gas temperature) and a pressure (inlet gas pressure) of a refrigerant sucked into the compressor and a pressure (discharged gas pressure) of a gas refrigerant discharged from the compressor.

It is noted here that even in an unsteady-state condition in which the refrigerating load abruptly varies, as to the inlet gas temperature, the inlet gas pressure and the discharged gas pressure, the detected value by the sensors are substantially equal to actual values, and accordingly, a discharged gas temperature can be exactly estimated under computation from the inlet gas temperature, the inlet gas pressure and the discharged gas pressure. Further, by calculating an injection quantity of the liquid refrigerant from an estimated discharged gas temperature, an appropriate quantity of the liquid refrigerant can be calculated. Thus, if the estimated discharged gas temperature exceeds a set temperature, by controlling the injection quantity of the liquid refrigerant, the liquid refrigerant can be injected by an appropriate quantity even in an unsteady-state condition.

In this case, in a steady-state condition in which a refrigerating load is stably maintained, the discharged gas temperature detected by the sensor is substantially equal to the actual value, and accordingly, it is desirable to carry out such control that the liquid refrigerant is injected into the compressor by a quantity based upon a detected value by the sensor. Specifically, there is provided a temperature sensor for detecting a temperature of a gas refrigerant discharged from the compressor, and the injection quantity of the liquid refrigerant into the compressor is controlled, depending upon a detected value by the temperature sensor if a deviation between the detected value by the sensor and the estimated temperature is smaller than a set value, but the injection quantity of the liquid refrigerant is controlled depending upon the estimated temperature if the deviation exceeds the set value.

Thus, according to the present invention, the discharged gas temperature can be controlled to the set temperature, irrespective of an operating condition.

Explanation will be hereinbelow made of preferred embodiments of the present invention with reference to the accompanying drawing, in which:

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a systematic view illustrating a refrigerating system in a first embodiment in which the present invention is applied;

FIG. 2 is a flow-chart for explaining control for injecting liquid refrigerant into a compressor; and

FIG. 3 is a systematic view illustrating a refrigerating system in a second embodiment in which the present invention is applied.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

Referring to FIGS. 1 and 2, explanation will be hereinbelow made of a first embodiment of a refrigerating system to which the present invention is applied. With reference to FIG. 1 which is a systematic view illustrating the refrigerating system in the first embodiment of the present invention, explanation will be explained in the embodiment of the refrigerating system which is applied in a refrigerator, but the present invention should not be limited to this embodiment, but it may be applied to a freezer, an air-conditioning system or the like.

Referring to FIG. 1, the refrigerating system used in the refrigerator, is composed of a scroll compressor (which will be hereinbelow referred simply to “compressor”) 10 sucking thereinto a refrigerant, for compressing the refrigerant, a condenser 12 for condensing and liquefying a gas refrigerant discharged from the compressor 10, an expansion valve 14 as a depressurizing means for depressurizing the refrigerant liquefied by the condenser 12, and an evaporator 16 for evaporating the refrigerant depressurized by the expansion valve 14, and the like. Further, a refrigerant pipe line 18 connects the condenser 12 to the evaporator 16 by way of the expansion valve 14. It is noted that any of various types of compressors may be used as the compressor 10 in addition to the scroll type compressor.

An inlet gas temperature sensor 24 for detecting a temperature of the refrigerant to be sucked into the compressor 10 (which will be hereinbelow referred to as “inlet gas temperature”) and an inlet gas pressure sensor 27 for detecting a pressure of the refrigerant to be sucked into the compressor 10 (which will be hereinbelow referred to as “inlet gas pressure”) are provided on the inlet side of the compressor 10. Further, a discharged gas pressure sensor 28 for detecting a pressure of the gas refrigerant discharged from the compressor 10 (which will be referred to as “discharged gas pressure”) is provided on the discharge side of the compressor 1.

The compressor 10 is injected thereinto with a liquid refrigerant by a liquid injection circuit as a liquid injection means. The liquid injection circuit is composed of an injection pipe line 20 which branches from the refrigerant pipe line 18 and which is connected to the intermediate pressure stage of the compressor 10, and a flow regulating valve 22 as a flow regulating means connected in the injection pipe line 20. In the intermediate pressure stage of the compressor, the refrigerant is under a compression stroke, that is, being compressed, and accordingly, the liquid refrigerant is injected into this stage by way of the injection pipe line 20. It is noted that as the flow regulating means, there may be used a plurality of fixed flow rate adjusters (for example, capillary tubes, which are changed over) and a solenoid valve which can adjust the flow rate stepwise. Further, there is provided a control unit 26 for delivering an instruction to the flow regulating valve 22 in accordance with detected values delivered from the inlet gas temperature sensor 24, an inlet gas pressure sensor 27 and the discharged gas pressure sensor 28.

Explanation will be hereinbelow made of the principal operation of the refrigerating system which constitutes the refrigerating cycle as stated above. The refrigerant sucked in the compressor is compressed and then discharged. The thus discharged liquid refrigerant is heat-exchanged with, for example, the atmospheric air so as to be condensed in the condenser 12. The thus condensed refrigerant is led through the refrigerant pipe line 18 and into the expansion valve 14 so as to be depressurized. The depressurized refrigerant is evaporated in the evaporator 16 by a secondary refrigerant (for example, the air). The evaporated refrigerant is returned into the compressor 10. The secondary refrigerant which has been cooled by the refrigerant in the evaporator 16 is led into the refrigerator. It is noted here that explanation has been made of the operation of the refrigerating cycle for cooling the inside of the refrigerator, the operation of a refrigerating cycle for heating a thermal load is basically similar as stated above, except that the stream of the refrigerant is led in a reversed direction by means a four-way selector valve.

Referring to FIG. 2, explanation will be made of the operation of control for injecting the liquid refrigerant into the compressor 10, according to the present invention, in an example of the injection into the compressor 10 upon a start of the refrigerating system. FIG. 2 shows a flow-chart of the control for injecting the liquid refrigerant into the compressor 10. The control program shown in this figure is packaged in the control unit 26.

As shown in FIG. 2, detected values from the sensors are taken into (S102). Specifically, an inlet temperature T1 detected by the inlet gas temperature sensor 24, an inlet gas pressure P1 detected by the inlet gas pressure sensor 27 and a discharged gas pressure P2 detected by the discharged gas pressure sensor 28 are taken into. A temperature T2 of the discharged gas is estimated under computation from the inlet gas temperature T1, the inlet gas pressure P1 and the discargd gas pressure P2 (S104). The thus estimated temperature T2 of the discharged gas is compared with a set discharge gas temperature T0 (S106). It is noted that the set temperature T0 has been previously determined in order to prevent deterioration of the refrigerant and lowering of the viscosity of a refrigerating machine oil contained in the refrigerant, and is set in a range, for example, 90 to 110 deg.C.

If the temperature T2 of the discharged gas is not less than the set temperature T0 at step 106, it is determined that the temperature T2 of the discharged gas should be lowered, and accordingly, a quantity Q (kg/sec) of liquid injection as an injection quantity of the liquid refrigerant is computed from a difference between the estimated temperature T2 of the discharged gas and the set temperature T0 (S108). An instruction corresponding to the thus computed liquid injection quantity Q (kg/sec) is delivered to the flow control valve 22 (S110). The flow control valve 22 is adjusted to a predetermined opening degree in accordance with the delivered instruction, and accordingly, the liquid refrigerant is injected into the intermediate pressure stage of the compressor 10 from the refrigerant pipe line 18. It is noted that if the temperature T2 of the discharged gas is lower than the set temperature T0 at step 106, the liquid injection quantity Q (kg/sec) may be reduced in accordance with a deviation between the temperature T2 of the discharged gas and the set temperature T0 (S107).

In order to explain the principle of estimation of the temperature T2 of the discharged gas, the energy balance of the compressor 10 is taken into consideration. That is, an input energy applied to the compressor 10 and an output energy delivered from the compressor 10 must be equal to each other, and accordingly, the energy balance can be exhibited by, for example, the following equation (formula) (1). Accordingly, the values at step 104 can be measured, except the temperature T2 of the discharged gas, as understood from the equation (1). Alternatively, they can be previously determined from the specification of the compressor 10. Thus, the temperature T2 of the discharged gas can be obtained from the formula (1). <Enthalpy of Inlet Gas>×<Refrigerant Circulation Quantity (kg/sec>+<Energy required for Compression>−<Enthalpy of Discharged Gas>×<Refrigerant Circulation Quantity (kg/sec)>=<Enthalpy of Liquid Refrigerant injected through Liquid Injection>×<Liquid Injection Quantity Q (kg/sec)>  (1)

Parameters in the formula (1) can be obtained as follows;

<Enthalpy of Inlet Gas> can be computed from the inlet temperature T1, the suction pressure P1 and the physical property of the refrigerant. Specifically, it is obtained by substituting the inlet temperature T1 and the suction pressure P1 to, for example, a Mollier Chart which is determined depending upon the physical property (for example, a kind of refrigerant such as R410). The Moller chart exhibits the refrigerating cycle with a relationship between enthalpy and pressure.

<Refrigerant Circulation Quantity (kg/sec)> can be obtained from an inlet gas volume (m³/sec), a volumetric efficiency (%) and an inlet gas density (kg/m³). It is noted here that the inlet gas density is calculated from the inlet gas temperature T1, the inlet gas pressure P1 and the physical property of the refrigerant. Further, the volumetric efficiency is an index of variation in volume of the refrigerant actually sucked into the compressor 10, which is caused by leakage of the refrigerant or the like, and which is determined by a specification of the compressor 10.

<Energy required for Compression> can be computed from an overall adiabatic pressure efficiency (%) of the compressor 10, the inlet gas temperature T1, the inlet gas pressure P1 and a specification of the compressor 10. It is noted that the overall adiabatic pressure efficiency (%) can be determined by the specification of the compressor 10. Further, instead of the computation, it may be obtained by measuring a power inputted to the compressor 10 with a measuring device.

<Enthalpy of Discharged Gas> can be obtained from the inlet gas pressure P1, the discharge gas temperature T2. At step S104, the discharged gas temperature T2 is the value which is estimated under computation.

<Enthalpy of Liquid Refrigerant injected through Liquid Injection> can be computed from a temperature of the liquid refrigerant injected into the compressor 10 and a physical property of the liquid refrigerant. It is noted here that the temperature of the injected liquid refrigerant can be obtained from the discharge pressure P2. Alternatively, it may be detected by a temperature sensor.

<Liquid Injection Quantity Q (kg/sec)> is initialized at the time of a start of the compressor 10 to zero, but during the operation of the refrigerating system, a direct liquid injection quantity Q (kg/sec) computed at step S110 can be used. In this embodiment, as to the inlet gas temperature T1, the inlet gas pressure P1 and the discharged gas pressure P2, since they exhibit substantially equal values between their detected values and their actual values even in an unsteady-state upon a start of the compressor or the like, an actual discharged gas temperature T2 can be estimated (anticipated) from the inlet gas temperature T1, the inlet gas pressure P1 and the discharged gas pressure P2. Accordingly, by controlling the liquid injection quantity Q, the liquid refrigerant can be exactly injected even in an unsteady-state condition. Further, by calculating the liquid injection quantity Q from the estimated gas temperature T2, an appropriate injection quantity of the liquid refrigerant can be injected into the compressor 10.

That is, in this embodiment, there can be carried out predictive control for controlling the liquid injection quantity Q (kg/sec) in accordance with the estimated discharge gas temperature T2 during operation of the refrigerating cycle. Accordingly, even when the temperature of the discharged gas is lowered through heat absorption by components (including the pipe line) making contact therewith during a period through which the discharged gas comes up to a measuring part such as the temperature sensor, the temperature of the discharged gas can be appropriately controlled, thereby it is possible to prevent deterioration of the refrigerant and a refrigerant machine oil due to overheating of the refrigerant gas. Accordingly, lubrication for a slide part of the compressor 10 can be ensured, thereby it is possible to restrain the compressor 10 from being seized. Further, there would not be caused affection by a delay in detection by the temperature sensor itself.

It is noted here that, instead of control of the liquid injection quantity Q (kg/sec) from a discharged gas temperature estimated during the operation of the refrigerating system, the discharged gasw temperature T₂ may be measured while the inlet temperature T1, the inlet pressure P1 and the discharge pressure P2 are gradually changed, and the thus obtained measured value may be stored in a memory of the control unit 26 as a data table. Further, during the operation of the refrigerating system, by collating the inlet temperature T1, the inlet pressure P1 and the discharge pressure P2 on the data table so as to estimate the discharge gas temperature T2, the liquid injection quantity Q (kg/sec) can be controlled.

Instead of controlling the liquid injection quantity Q (kg/sec) depending upon the estimated discharged gas temperature T2 during the operation of the refrigerating system, there may be used a data table on which measured values of the discharged gas temperature T2 obtained by gradually changing the inlet gas temperature T1, the inlet gas pressure P1 and the discharged gas pressure P2 are set and which is stored in a memory in the control unit 26. Further, during the operation of the refrigerating system, the inlet gas temperature T1, the inlet gas pressure P1 and the discharged gas pressure P2 which have been detected are collated on the data table so as to estimate the discharged gas temperature T2 with which the liquid injection quantity Q (kg/sec) may be controlled.

It may be considered to incorporate a temperature sensor in the compressor, just downstream of the compression stroke, in order to reduce a delay in the control, in addition to this embodiment. However, it should be incorporated in a pressure-proof container of the compressor 10, and accordingly, there would be caused a complicated structure or lowering of sealing ability, resulting in deterioration of the reliability of the compressor 10. In view of this point, according to this embodiment, even with no provision of the temperature sensor, the temperature of the discharged gas from the compressor 10 can be estimated.

Further, in this embodiment, although explanation has been made of such a configuration that R410 (Weight Ratio of R32:50%/R125:50%) is used, there may be used various kinds of refrigerant. However, it is noted that R410A has a lubricity which is not high in comparison with that of, for example, R22 or R12 containing chlorine atoms, and has a tendency of readily increasing its temperature, in comparison with R404A (weight ratio of R125:44%/R143a:52%/R134a:4%). Thus, by applying the present invention to a refrigerating system using R10A, the present invention further exhibits its technical effects and advantages.

Second Embodiment

Explanation will be made of a second embodiment to which the present invention is applied, with reference to FIG. 3 which is a systematic view illustrating a refrigerating system in this embodiment of the present invention. The configuration of this second embodiment is substantially the same as that of the first embodiment, except that a steady-state condition and an unsteady state condition are determined, and then the control modes of the liquid injection quantity are changed over, depending upon a result of the determination.

Referring to FIG. 3, a discharge temperature sensor 30 is provided on the discharge side of the compressor 10 in the refrigerating system which should be compared with the first embodiment shown in FIG. 1. In this second embodiment, a detected value of a discharged gas temperature T₃ is delivered to the control unit 26. Further, similar to the first embodiment, the discharged gas temperature T₂ is also estimated by the control unit 26 in order to obtain a temperature difference between the discharged gas temperatures T2 and T3. If the thus obtained temperature difference is smaller than a preset value, it is determined that the refrigerating system is of steady-state. Thus, the liquid injection quantity Q (kg/sec) can be controlled, depending upon the discharged gas temperature T3 measured by the discharge temperature sensor 30. It is noted that the steady-state condition is such that the refrigerating system is operated stably, that is, for example, the temperature of the discharged gas is substantially equal to that of the pipe line or the like which make contact with the discharged gas.

Meanwhile, if the temperature difference between the discharged gas temperatures T2 and T3 is not less than the preset value, it is determined that the refrigerating system is of unsteady-state. Thus, an actual temperature T2 of discharged gas is estimated under computation from the inlet gas temperature T1, the inlet gas pressure P1 and the discharged gas pressure P2, as stated in the first embodiment, and the liquid injection quantity Q (kg/sec) is controlled, depending upon the estimated temperature T₂.

That is, when the refrigerating system is of steady-state, the discharged gas temperature T₃ which is a detected value becomes near an actual discharged gas temperature with a high degree of possibility, in comparison with the discharged gas temperature T₂, and accordingly, the control based upon the discharged gas temperature T3 is preferentially carried out. Meanwhile, then the refrigerating system is of unsteady-state, the discharged gas temperature T2 which is an estimated value becomes near an actual discharged gas temperature with a high degree of possibility, in comparison with the discharged gas temperature T3, and accordingly, prediction control stated in the first embodiment is preferentially carrier out.

According to this embodiment, even with the repetitions of state transition of the refrigerating system from the steady-state condition to the unsteady-state condition or from the unsteady-state condition to the steady-state condition, since the liquid refrigerant can be exactly injected into the compressor 10 by an appropriately quantity, it is possible to further restrain the discharged gas temperature from exceeding the set temperature T₀.

Although explanation has been made of the present invention in the form of the first and second embodiments, the present invention should not be limited to these embodiments. For example, although the time of a start of the compressor has been explained as an example of the unsteady-state condition, the present invention can be also applied for such a case that a casing in the refrigerator is opened or closed. Namely, the present invention may be applied to such a case that the pressure and the temperature of the refrigerant sucked into the compressor 10 vary-since the refrigeration load relatively abruptly varies.

Further, in such a case that a plurality of compressors 10 are incorporated in a refrigerating system or that a multi-system in which a plurality of refrigerating systems are incorporated, is configured, since the quantity of the refrigerant through circulation abruptly varies due to the repetitions of a start and a stop of any of compressors or due to an increase or a decrease of the number of refrigerating systems on operation, by applying the present invention, it is possible to further restrain the discharged gas temperature from exceeding the set temperature T0.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A refrigerating system comprising: a compressor sucking thereinto a refrigerant, for compressing the refrigerant, a condenser for condensing the refrigerant discharged from the compressor, a liquid injection means for injecting a liquid refrigerant into the compressor, sensors for respectively detecting a temperature and a pressure of the refrigerant sucked into the compressor, and a pressure of the refrigerant discharged from the compressor, a control means for controlling an injection quantity of the liquid refrigerant injected into the compressor, depending upon detected values delivered from the sensors, wherein the control means estimates a temperature of a gas refrigerant discharged from the compressor from the detected values delivered from the sensors, and delivers an instruction for controlling the injection quantity of the liquid refrigerant, depending upon the estimated temperature, to the liquid injection means.
 2. A refrigerating system comprising: a compressor sucking thereinto a refrigerant, for compressing the refrigerant, a condenser for condensing the refrigerant discharged from the compressor, a depressurizing means for depressurizing the condensed refrigerant, an evaporator for evaporating the depressurized refrigerant, a liquid injection means for injecting a liquid refrigerant into the compressor, sensors for respectively detecting a temperature and a pressure of the refrigerant sucked into the compressor, and a pressure of the refrigerant discharged from the compressor, a control means for controlling an injection quantity of the liquid refrigerant injected into the compressor, wherein the control means estimates a temperature of the refrigerant discharged from the compressor, from detected values delivered from the sensors, and delivers an instruction for controlling the injection quantity of the liquid refrigerant, depending upon the estimated temperature, to the liquid injection means.
 3. A refrigerating system as set forth in claim 1, wherein the control means comprises a means for comparing the estimated temperature and a set temperature with each other, and a computing means for computing an injection quantity of the liquid refrigerant from the estimated temperature if the estimated temperature is higher than the set temperature.
 4. A refrigerating system as set forth in claim 2, wherein the liquid injection means comprises an injection passage through which the liquid refrigerant flows, and a flow adjusting means connected in the injection passage, for changing the injection quantity of the liquid refrigerant, depending upon the instruction delivered from the control part.
 5. A refrigerant system as set forth in claim 1, wherein an additional temperature sensor for detecting a temperature of a gas refrigerant discharged from the compressor is provided, and the control means controls the injection quantity of the liquid refrigerant, depending upon the detected value by the temperature sensor if a deviation between a detected value by the second temperature sensor and the estimated temperature is lower than a set value, but the control means controls the injection quantity of the liquid refrigerant, depending upon the estimated temperature, if the deviation is not less than the set value. 